1. Field of the Invention
The invention relates to an X-ray examination apparatus which includes an X-ray source and a diaphragm unit which is connected to the X-ray source and is provided with shutters for limiting a radiation cone beam emanating from a focal spot of the X-ray source, and also includes a light source for generating a light cone beam which traverses the shutters via a reflector device. The invention also relates to a diaphragm device for an X-ray source.
2. Description of the Related Art
An X-ray examination apparatus and a diaphragm unit of the kind set forth are known from U.S. Pat. No. 5,844,962.
Therein, the light cone serves as an aid which facilitates the adjustment by the user of the irradiated field exposed to the X-rays during a subsequent X-ray exposure. The light cone then illuminates either the patient to be examined or, in the case of an X-ray examination apparatus provided with a grid drawer, the grid drawer when the X-ray source and the grid drawer with the film to be exposed are temporarily pulled to a position to the side of the table top on which the patient is accommodated. The illuminated surface should then correspond to the surface exposed to the cone beam of the X-ray source during a subsequent X-ray exposure.
The light source is then situated at the same optical distance from the shutter plates as the focal spot of the radiation source. The light source should be as inexpensive as possible, have a long service life and a high brightness, and the light cone defined thereby should correspond as accurately as possible to the radiation cone formed during a subsequent X-ray exposure. The dimensions of light sources, i.e. the structure emitting the light, for example the filament of the light source, however, are large in comparison with those of the focal spot of the X-ray source. Consequently, the surface illuminated by the light source is larger than the surface subsequently exposed to the X-rays.
In order to match the surface irradiated by the X-ray source and the surface irradiated by the light source, the known X-ray examination apparatus is provided with a motor drive for the shutters, which drive is controlled in such a manner that during the adjustment by means of the light source the diaphragm aperture is smaller than during a subsequent X-ray exposure. This solution necessitates the presence of an appropriately controlled motor drive.